There has been a belt-type continuously variable transmission which shifts the gear ratio by changing, by mean of hydraulic pressure, the groove widths of a drive pulley and a driven pulley having a metal belt wound therearound, and in which three hydraulic oil chambers are formed between a movable pulley half and a pulley cover, and three pistons respectively facing these three hydraulic oil chambers are driven by means of hydraulic pressure to bias the movable pulley half toward its fixed pulley half. This continuously variable transmission has been publicly known by Japanese Patent Application Laid-open No. 2009-264427.
FIG. 4 shows a pulley cover 01, a forged product, described in Japanese Patent Application Laid-open No. 2009-264427. The forged pulley cover 01 includes a disk-shaped side wall 02, an annular partition wall 03, and an annular peripheral wall 04. A first hydraulic oil chamber 05 is formed at an inner side, in a radial direction, of the partition wall 03, while a second hydraulic oil chamber 06 is formed at an outer side, in the radial direction, of the partition wall 03. An oil hole 07 allowing communication between the first and second hydraulic oil chambers 05, 06 is machined to penetrate through the partition wall 03. When the oil hole 07 is machined in the forged pulley cover 01, the oil hole 07 needs to be formed inclining at an angle θ to the radial direction which is centered on an axis L. This is because machining from the radially inner side of the partition wall 03 causes interference between a portion of the partition wall 03 on the opposite side of the axis L and a tool such as a drill, whereas machining from the radially outer side of the partition wall 03 causes interference between the peripheral wall 04 and a tool such as a drill.
When the oil hole 07, which has a given diameter D, is inclined at the angle θ to the radial direction, a dimension D′ of the oil hole 07 in the direction of the axis L becomes larger than the diameter D, causing a problem that the dimension of the pulley cover 01 in the direction of an axis L is increased accordingly.